B-C-N film with a ~450 nm thickness was prepared on a (100) oriented silicon wafer (4 cm × 4 cm) by
unbalanced magnetron sputtering of a B4C target with a unipolar pulsed DC substrate bias. At a substrate
bias of &#8722;250 V, a cubic boron nitride (cBN) phase appeared in the B-C-N film when the nitrogen content
was over 6.7 vol% in Ar-N2 reactive gases. For the B-C-N film deposited on unipolar pulsed DC biased Si
substrate with Ar-16.7%N2 reactive gas, the content and formation behavior of the cBN phase along with
the film thickness were critically dependent on the substrate position due to the difference in ion flux. In
contrast to the circular central region of a substrate 2.5 cm in diameter, where cBN was nucleated and
grown on hexagonal boron nitride (hBN) in a layered manner, the cBN phase was co-grown with the hBN
phase and was surrounded by hBN at the circumference region of the circle. Only hBN was observed at
the outer region of the circle. The microstructure of B-C-N film in which cBN is surrounded by hBN is
believed to be effective in reducing residual stress developed by the nucleation of a cBN phase.